A trait displays continuous phenotypic variation and is spread across a gradient. Usually, the inheritance of this trait can be described as:
1. dominant-recessive inheritance
2. multiple-allele inheritance
3. polygenic inheritance
4. sex-linked inheritance
An F2 phenotypic ratio of 1: 4: 6: 4: 1 from a cross AaBb X AaBb is expected in the case of:
1. | Dominant epistasis | 2. | Complementary genes |
3. | Polygenic inheritance | 4. | Independent assortment |
1. | 2 genes | 2. | 3 genes |
3. | 4 genes | 4. | 6 genes |
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1. | 6/64 | 2. | 15/64 |
3. | 20/64 | 4. | 1/64 |
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I: | Polygenic inheritance takes into account the influence of the environment. |
II: | In a polygenic trait, the phenotype reflects the contribution of each allele, i.e., the effect of each allele is additive. |
III: | The normal distribution curve is bell-shaped in polygenic inheritance. |
IV: | It is also known as quantitative inheritance. |
1. | 0 | 2. | 1 |
3. | 3 | 4. | 4 |
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Occasionally, a single gene may express more than one effect. The phenomenon is called:
1. | multiple allelism | 2. | mosaicism |
3. | pleiotropy | 4. | polygeny |
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The physiological basis of pleiotropy is:
1. | lack of independent assortment in linked genes |
2. | separation of homologous chromosomes at anaphase I in meiosis I |
3. | dominance is not an autonomous feature of an allele |
4. | inter-relationships of many metabolic pathways in the living organisms |
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I: | Where a single gene can exhibit multiple phenotypic expressions, such a gene is called a pleiotropic gene. |
II: | The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes. |
III: | Phenylketonuria is caused by a defect in the gene that codes for the enzyme phenylalanine hydroxylase and manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation. |
1. | Statement I is correct, Statement II is correct, Statement III is incorrect. |
2. | Statement I is incorrect, Statement II is correct, Statement III is incorrect. |
3. | Statement I is correct, Statement II is incorrect, Statement III is correct. |
4. | Statement I is correct, Statement II is correct, Statement III is correct. |
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